The present invention relates to a coordinates input device, a coordinates input method with which the coordinates of a manually specified point can be input and a display board system which uses such a coordinates input device.
Presently there is known a display board system in which a freehand information (e.g. characters, drawings etc.) written on the surface of the board (hereafter called as writing surface), which surface defines an entry area, can be input into a computer or so in real time. Such a display board system uses a coordinates input device which detects the coordinates of the position of the pen where the pen touches the writing surface and successively inputs these coordinates into a computer or the like.
In one of the methods of detecting coordinates by the coordinates input device, light is made use of. For instance, light is irradiated on the entire surface of the writing surface and the reflected light is detected. When something is written on the writing surface, the pen hinders the light and the coordinates of the position of the pen can be obtained from the detected reflected light. Such a method is disclosed in Japanese Patent Laid-Open Publication No. HEI 9-91094. In the Japanese Patent Laid-Open Publication No. HEI 9-91094 there is disclosed a configuration in which a light source is driven using a driving unit in such amanner that the light is irradiated on the entire surface of the writing surface (which may be a touch panel) and the writing surface can be scanned with the light.
There is a further simplified configuration obtained by removing a driving unit from the device described above. In this configuration, light emitted from a light source is spread in a fan shape using a lens or the like so as to cover an entire area of the writing surface. FIG. 13 explains the principles of this method in a simple manner. The configuration shown in the figure comprises a panel 100 as a writing surface, a reflector 2 provided on the three sides of the panel 100, and a light source R provided at the lower-right corner and a light source L provided at the lower-left corner of the panel 100. Point P(xp, yp) on the panel 100 indicates a position of a pen tip on the panel 100.
The light emitted from any of the light sources R and L is spread by a lens (not shown) placed on the front surface of each of the light sources R and L and becomes a light flux in a fan shape (hereafter called as fan-shaped light flux) having a central angle of 90 degrees. This fan-shaped light flux is reflected by the reflector 2 provided at the edge of the panel 100. This reflector 2 is designed in such a way that a fan-shaped light flux is reflected along an optical axis which is identical to the one along which the light came in. Therefore, the fan-shaped light flux in reflected back towards the light sources R and L along an optical axis which is identical to the one along which the light came in. This reflected light is directed towards a not shown light receiver, for instance, using a not shown mirror provided on this optical axis and the light is detected.
When the tip of the pen tip is placed on the position of point P on the panel 100, a light beam passing through the point P of the fan-shaped light flux is reflected by the pen tip and it does not reach the reflector 2 (in the specification, this situation will be described as xe2x80x9cthe light beam is blocked by the pen tipxe2x80x9d) Therefore, only the reflected light of the light beam passing through the point P of the fan-shaped light flux can not resultantly be detected by the light receiver. By using, for example, a CCD line sensor as the light receiver, optical axis of the light beam which is not received can be identified from the whole reflected light beams.
Since the optical axis of the reflected light is identical to that of the emitted light and the point P exists on the optical axis of a light beam which is not detected, a angle of emission of the light beam passing through the point P can be calculated from the optical axis of the reflected light which is not detected. Therefore, angle of emissions xcex8L and xcex8R can be calculated from the results of reception of light by the two light receivers, and optical axes aL and aR can be calculated from those angle of emissions. Further, coordinates (xp, yp) of the point P, which is an intersection point of the optical axes aL and aR can also be calculated.
More specifically, the coordinates (xp, yp) of the point P can be calculated as described below. Namely,
xp=(tan xcex8Rxc2x7W)/(tan xcex8R+tan xcex8L)xe2x80x83xe2x80x83(1)
  "AutoLeftMatch"                                                                                          y                  p                                =                                                      (                                          tan                      ⁢                                              xe2x80x83                                            ⁢                                                                        θ                          R                                                ·                        tan                                            ⁢                                              xe2x80x83                                            ⁢                                                                        θ                          L                                                ·                        W                                                              )                                    /                                      (                                                                  tan                        ⁢                                                  xe2x80x83                                                ⁢                                                  θ                          R                                                                    +                                              tan                        ⁢                                                  xe2x80x83                                                ⁢                                                  θ                          L                                                                                      )                                                                                                                          =                                                                            x                      p                                        ·                    tan                                    ⁢                                      xe2x80x83                                    ⁢                                      θ                    L                                                                                                                        (            2            )                    ⁢                      xe2x80x83                              
Where W is a distance between centers of the light sources R and L.
Thus, the coordinates input device reads a locus of a pen tip by successively reading coordinates of the pen tip moving along the panel 100 and can automatically record contents written in the panel 100.
The distance W between centers of the light sources R and L is used in equations (1) and (2) for calculating coordinates (xp, yp). However, the distance W may slightly vary depending upon the accuracy with which the light sources R and L are attached to the panel 100. Further, the distance W may slightly vary depending upon the accuracy with which the dimensions of the panel 100 have been maintained during manufacture. If the distance W varies, the variation is also reflected into the results of the equations (1) and (2). Therefore, there is a great probability that coordinates (xp, yp) can not accurately be calculated.
In addition, the material used to manufacture the panel 100 can easily be machined and is low cost, however, it can easy get deformed (expand or shrink) depending upon the surrounding temperature. Therefore, there is great possibility that the coordinates (xp, yp) may change depending on the surrounding temperature.
In order to solve the above-described problems, i.e. to keep the value of W to be as a designed value at any time, it is required to improve accuracy of attachment of the light sources R and L to the panel 100. Further, improve the accuracy in maintaining the dimensions of the panel 100, and to manufacture the panel 100 with a material which does not deform much depending upon the temperature. However, most of the technologies that improve accuracy of attachment and accuracy of dimensions requires sense and experience of a skilled engineer, therefore it has been thought that the technology is generally inappropriate to be applied to products to be mass-produced. Regarding manufacturing the panel 100 with a material which does not deform much depending upon the temperature, if such material is used then the easiness of machining may be damaged or the cost of manufacturing may be increased.
The present invention has been made for solving the problems described above, and it is a first object of the present invention to provide a coordinates input device and a display board system enabling an accurate detection of an obstacle.
In addition, it is a second object of the present invention to provide a coordinates input device and a display board system enabling accurate detection of the obstacle any time no matter how much the material used for manufacturing the entry area gets deformed.
The problems described above can be solved by the means described below.
The coordinates input device according to one aspect comprises a light emitter which emits a light flux to a specified entry area; a light receiver which receives the light flux emitted from the light emitter; a coordinate calculator for calculating coordinates of an obstacle in the light flux on the entry area based on the light flux received by the light receiver and the dimensions of the entry area; and an entry-area measurement unit for measuring the dimensions of the entry area used for calculating the coordinates by the coordinate calculator. The coordinates input device obtains dimensions of an entry area of the coordinates input device at any time by measuring and calculating dimensions of the entry area required for calculating coordinates. Thus, accurate dimensions of the entry area can be obtained without improving accuracy of attaching the optical units thereto or accuracy of dimensions of an entry area.
A display board system according to another aspect of this invention comprising a display unit for displaying characters and images thereon and the coordinates input device according to the above invention to be provided on the front surface of the display unit. Because the coordinates input device has a configuration as described above, accurate dimensions of the entry area can be obtained without improving accuracy of attaching the optical units thereto or accuracy of dimensions of an entry area.